Mayer says that Yahoo released "Yahoo Stream Ads" in May, which take text ads and put them in the news stream on Yahoo.com. She says you can expect more of that on Tumblr. On Tumblr, there is the dashboard, which is like Facebook's News Feed or inbox. Today, Tumblr does some advertising there. Yahoo would like to "introduce a very light ad load" there. Yahoo also might work with some bloggers who want ads on their blogs. That would only be done with permission.

Mayer says the ad units will be native and follow the form and function of Tumblr.

Advertisers are already salivating at the thought of getting more exposure in front of Tumblr's massive audience. Ad Age noted:

... according to Chris Copeland, CEO of Group M Next. "Any time you go from the startup world to established companies with good infrastructure around technology and data, there's an opportunity to move forward in helping brands understand what they're getting from you," Mr. Copeland said.

"What makes Tumblr such an attractive acquisition is it has so much credibility among this audience that Yahoo and others are seeking -- this 18-to-24 sweet spot," said Ming Linsley, MEC's senior director of social media. "The concern everyone has is whether or not Tumblr will lose its credibility if it's acquired by Yahoo."

Tumblr sales chief Lee Brown already said last year that's working with advertisers who want reach and frequency — mass exposure, in plain English — on Tumblr. "[Some buyers] just want to buy units for reach and frequency. I’m working through that with them now," he told Adweek.

We noted earlier that Tumbr has made half a dozen significant moves — including adding mobile ads — in recent months to make itself attractive to advertisers, and the company believes it will be profitable soon. It had only $13 million in revenue last year.

“They have to balance keeping those users actively using Tumblr, while at the same time adding advertising and putting monetization around it,” he said. “Those are very difficult tasks to balance against each other.”

Difficult tasks, indeed. But note that everyone — Karp's new boss, Karps' sales chief, advertisers, and Wall Street — are all agreed on the same thing.